\setlength{\tabcolsep}{20pt}
\caption{Party classification}
\begin{tabular}{lclc}
\toprule
\multicolumn{2}{c}{\textbf{Leftist parties}} & \multicolumn{2}{c}{\textbf{Non-leftist parties}}  \\
\midrule
\multicolumn{1}{c}{Party} & \multicolumn{1}{c}{Source} & \multicolumn{1}{c}{Party} & \multicolumn{1}{c}{Source} \\
\midrule
PV & Zucco and Power (2018) & DEM/PFL & Zucco and Power (2018) \\
PT & Zucco and Power (2018) & MDB/PMDB & Zucco and Power (2018) \\
PSOL & Zucco and Power (2018) & PP & Zucco and Power (2018) \\
PSB & Zucco and Power (2018) & PR & Zucco and Power (2018) \\
PPS/CID & Zucco and Power (2018) & PRB & Zucco and Power (2018) \\
PDT & Zucco and Power (2018) & PSDB & Zucco and Power (2018) \\
PCdoB & Zucco and Power (2018) & PSL & Zucco and Power (2018) \\
PPL & Foro de São Paulo & PTB & Zucco and Power (2018) \\
PSTU & Baker and Greene (2011) & PRONA & Baker and Greene (2011) \\
PMN & Baker and Greene (2011) & PRP & Baker and Greene (2011) \\
PCO & Baker and Greene (2011) & PRTB & Baker and Greene (2011) \\
PCB & Baker and Greene (2011) & PSC & Baker and Greene (2011) \\
 &  & DC/PSDC & Baker and Greene (2011) \\
 &  & PODE/PTN & Baker and Greene (2011) \\
 &  & PTdoB  &  \\
 &  & PAN &  \\
 &  & PHS &  \\
 &  & PL &  \\
 &  & PSD &  \\
 &  & PTC &  \\
 &  & PEN &  \\
 \bottomrule
\end{tabular}
